The present invention relates to cleanable, fiber glass ducts for conveying air which are used in heating, ventilating and air conditioning systems.
It is common practice to use fiber glass duct liners in heating, ventilating and air conditioning systems. As discussed in Terry et al, U.S. Pat. No. 4,990,370, column 1, lines 33-50, the interior surfaces of these fiber glass duct liners, which are relatively low in density when compared to fiber glass ducts, are either coated with a rubberized or plastic material or a facing is applied to the surface to prevent portions of the duct liner from breaking away or flaking off due to erosion by the air stream within the duct liner. Without the coating, loose particles of dust and dirt, in the air stream being conveyed, strike the interior surface of the duct liner causing erosion so that portions of the duct liner break away or flake off. However, the coating is only sufficient to prevent the erosion of the interior surface of the duct liner and does not form the smooth, durable surface required to withstand the cleaning of the interior surface of the duct liner by maintenance personnel using conventional commercial cleaning methods.
Fiber glass air ducts are also used in heating, ventilating and air conditioning systems. These air ducts are formed from high density fiber glass duct boards having a density of at least 3.5 pounds per cubic foot as compared to a density of 1.5 pounds per cubic foot for low density duct liners. The duct boards are formed by compressing blankets of resin coated glass fibers to an appropriate thickness and density and curing the resin binder. Due to the high density and the heavy resin binder content on the interior surface of the duct boards forming the air duct, the high density fiber glass ducts formed from the duct boards do not require a coating or facing on their interior surfaces to prevent erosion by the air stream. However, like the duct liners discussed above, the prior art air ducts have not had an interior surface suitable for cleaning by conventional industrial or commercial cleaning methods.
With recent developments in air quality measurement devices and an overall increase in environmental awareness, there has been an increased interest in the air quality in all types of buildings employing heating, ventilating and air conditioning systems. While in service, especially when the air filtration system is not properly maintained, the interior air conveying surfaces of air ducts pick up dust and become increasingly dirty. The accumulation of dust on the interior surfaces of ducts uses been identified as a possible nutrient source for microbiological growth. The growth of microbes in an a heating, ventilating and air conditioning system may compromise the indoor air quality of the building or home served by the system. Accordingly, there has been a need to provide a cleanable interior surface for air ducts.
The interior surfaces of sheet metal air ducts are often cleaned with rotating brushes having plastic bristles six inches to a foot long. Another method of cleaning air ducts uses industrial type vacuum cleaners. In addition, it is common to clean the interior surfaces of sheet metal air ducts with liquid chemical disinfectants to remove microbiological growth from the interior surface of the duct.
Fiber glass air ducts not only effectively convey the air in a heating, ventilating and air conditioning system, they also, unlike sheet metal air ducts, provide an acoustical benefit by reducing the transmission of sound. While fiber glass does not support mold growth and the use of liquid chemical disinfectants on the interior surface of fiber glass ducts is not necessary, the cleaning of uncoated fiber glass air ducts to remove dust and dirt by the methods discussed above can result in damage to the interior surface of an uncoated fiber glass air duct by puncturing and/or wearing away the interior surface of the duct. Accordingly, there has been a need to provide a cleanable interior surface for fiber glass air ducts that can be subjected to normal commercial cleaning methods.